This project seeks to determine how trace gases are exchanged
between the lower atmosphere (the troposphere) and the upper
atmosphere where the ozone layer is located (the
stratosphere). This is critical to assessing the effects of
natural and human-induced surface emissions on the potential for
ozone depletion and global warming. To develop an understanding
of transport processes in the lower stratosphere and at its
lower boundary, specific scientific questions are addressed: (1)
how does air move upward into the stratosphere in the tropics?
(2) can these processes of upward movement explain the extreme
dryness of the stratosphere? (3) what is the nature and
importance of wave motions produced by rapidly rising air in the
tropics? and (4) how does air move between the tropics and
midlatitudes in the stratosphere?

The approach involves the analysis of ER-2 measurements from
data obtained from the Stratosphere-Troposphere Exchange Project
(STEP), with additional aircraft data from the Airborne
Antarctic Ozone Experiment and the Airborne Arctic Stratosphere
Expedition. So far, the data from STEP have (1) provided
explanations for how tropical clouds move air from the
troposphere to the stratosphere; (2) shown that the tops of
these clouds are dry enough to account for low stratospheric
humidities; (3) measured wavelike structures produced above
tropical clouds; and (4) shown that other wavelike structures
can move stratospheric air from the tropics to the midlatitudes.